rcutorture: Add test of holding scheduler locks across rcu_read_unlock()

Now that it should be safe to hold scheduler locks across
rcu_read_unlock(), even in cases where the corresponding RCU read-side
critical section might have been preempted and boosted, the commit adds
a test of this capability to rcutorture.  This has been tested on current
mainline (which can deadlock in this situation), and lockdep duly reported
the expected deadlock.  On -rcu, lockdep is silent, thus far, anyway.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 5453bd5..b348cf8 100644 (file)
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1147,6 +1147,7 @@ static void rcutorture_one_extend(int *readstate, int newstate,
                                  struct torture_random_state *trsp,
                                  struct rt_read_seg *rtrsp)
 {
+       unsigned long flags;
        int idxnew = -1;
        int idxold = *readstate;
        int statesnew = ~*readstate & newstate;
@@ -1181,8 +1182,15 @@ static void rcutorture_one_extend(int *readstate, int newstate,
                rcu_read_unlock_bh();
        if (statesold & RCUTORTURE_RDR_SCHED)
                rcu_read_unlock_sched();
-       if (statesold & RCUTORTURE_RDR_RCU)
+       if (statesold & RCUTORTURE_RDR_RCU) {
+               bool lockit = !statesnew && !(torture_random(trsp) & 0xffff);
+
+               if (lockit)
+                       raw_spin_lock_irqsave(&current->pi_lock, flags);
                cur_ops->readunlock(idxold >> RCUTORTURE_RDR_SHIFT);
+               if (lockit)
+                       raw_spin_unlock_irqrestore(&current->pi_lock, flags);
+       }
 
        /* Delay if neither beginning nor end and there was a change. */
        if ((statesnew || statesold) && *readstate && newstate)